Proximity fuze improvement

ABSTRACT

Projectiles utilizing proximity fuzes wherein the windshield structure thereof is capable of withstanding the buildup of static electrical charges on the surface thereof resulting in the prevention of premature functioning of said fuzes comprising in combination a conical windshield portion and a cylindrical base portion. The conical windshield comprises an electrically conductive surface capable of withstanding and rapidly dispersing electrical charges on the surface and having a surface resistivity of between about 1.0 and 200 megohms per square.

United States Finger et a1.

atent [1 1 [451 Oct. 1, 1974 1 PROXIMITY FUZE IMPROVEMENT [75]Inventors: Daniel W. Finger; Gwendolyn B.

Wood, both of Bethesda, Md; Roy F. High, Washington, DC; Edwin H.Harrison, Jr., Arlington, Va.

[73] Assignee: The United States of America as represented by theSecretary of the Army, Washington, DC.

22 Filed: Oct. 31, 1972 21 Appl. No.: 302,456

[52] US. Cl. 102/70.2 P, 102/105, 343/841, 343/872 [51] Int. Cl. F42c19/04, HOlq 1/42 [58] Field of Search l02/70.2 P, 105; 325/357; 343/841,842, 872, 873

[56] References Cited UNITED STATES PATENTS 2,509,903 5/1950 Brode et all02/70.2 P 2,583,540 l/l952 Bennett 343/841 2,962,717 11/1960 Kofoid343/872 3,152,547 10/1964 Kyle l02/70.2 P

3,292,544 12/1966 Caldwell et al. 102/105 3,336,873 8/1967 Wilford l102/105 3,555,550 1/1971 Walters 102/105 3,616,140 10/1971 Copeland eta1 102/105 R25,417 7/1963 Amason 343/872 Primary Examiner-Benjamin A.Borchelt Assistant ExaminerC. T. Jordan Attorney, Agent, or Firm-EdwardJ. Kelly; Saul Elbaum [5 7 ABSTRACT Projectiles utilizing proximityfuzes wherein the windshield structure thereof is capable ofwithstanding the buildup of static electrical charges on the surfacethereof resulting in the prevention of premature functioning of saidfuzes comprisingin combination a conical windshield portion and acylindrical base portion. The conical windshield comprises anelectrically conductive surface capable of withstanding and rapidlydispersing electrical charges on the surface and having a surfaceresistivity of between about 1.0 and 200 megohms per square.

12 Claims, 1 Drawing Figure PROXIMITY FUZE IMPROVEMENT The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States of America for governmental purposes without thepayment of royalty thereon.

BACKGROUND OF THE INVENTION This invention relates essentially toprojectiles utilizing proximity fuzes and more particularly toprojectiles wherein the Windshields thereof are constructed in such amanner so as to prevent misfirings of proximity fuzes located therein.

The use of proximity fuzes in artillery projectiles have not been toosuccessful due to significant numbers of premature firings. Theseproblems were believed to be due to the buildup of static electricity onthe surface of the windshield and projectile thereby causing themisfirings.

Attempts to overcome these problems have not been successful up untilthis time. Recent laboratory tests indicate that an artillery projectilestrikes numerous particles during flight, e.g., dust particles and icecrystals, which comprise some clouds, thereby causing the projectile tobecome electrically (i.e., either positively or negatively) charged. Asthe electric potential increases to a point on the order of about 100 to700 kilovolts, a corona discharge occurs at the sharpest points on theprojectile, e.g., points A and B, as illustrated in the accompanyingdrawings (at B if windshield is conductive, at A and B if windshield isinsulator or semiconductor).

When a corona discharge occurs at position B, as per the attacheddrawings illustrating a typical artillery projectile having a metal fuzebody 4 and steel projectile casing 5, it has been found that arcingresults at the various gaps l in the segmented antenna 2. This arcingcreates high amplitude fast rise time pulses which pass into the fuzefiring circuit, thereby causing premature functioning of the projectile.

The effects of the buildup of electrical charges on the surface ofartillery projectiles is entirely different from the effects ofelectrical charge buildup on plastic enclosures or radomes of aircraft.In the latter, radar and other directional equipment are usually storedfor navigational purposes within the radome of an aircraft. Whenelectrical charges build up on the surface of a radome, this buildupusually results in the emission of signals tending to have adverseeffects on the navigation of the aircraft. In order to avoid theseproblems and control the electrical charge buildup on the surface ofaircraft, and particularly radomes, certain methods have been employedfor reducing the electrical charges in a controlled manner, e.g., byplacing discharge wicks on the wings, stroke guiding systems, exposedgrounded metal buttons, stroke diverting rods, diverter strips acrossradome surface (thin metal strips), etc. However, these methods havenever been adapted to preventing or modifying corona discharges onprojectiles or missiles containing proximity fuzes because the cause ofmisfirings have never been found to be due to the buildup of electricalcharges on the surface of nose cones, but only recently, to an entirelydifferent phenomena as will be discussed herein. When corona dischargesresult due to the buildup of electrical charges on the surface of thenose cone, various coatings and methods conventionally utilized todissipate the electrical charges on aircraft radomes cannot be adaptedfor use on projectiles due to the inability of these coatings towithstand high temperatures and velocities. In this regard, it is notedthat coatings on aircraft radomes are not satisfactorily resistant towithstand high temperatures on the order of 450-C. and velocities on theorder of 3,000 feet per second. In fact, the conventional urethanecoatings employed on aircraft radomes are not sufficiently ablationresistant for use on artillery projectiles and missiles.

A great need therefore exists for the development of artilleryprojectiles and missiles utilizing proximity fuzes that are capable offunctioning without premature functioning of the fuze firing circuit.

OBJECTS OF THE INVENTION Accordingly, it is a significant object of thepresent invention to provide an artillery projectile or missile having aproximity fuze therein which is capable of being utilized withoutsufficient electrostatic charge buildup on the nose cone thereof,thereby causing the premature functioning of the proximity fuzes.

Consistent with the primary object of this invention, it is also asignificant object of this invention to provide a means for dissipatingthe electrostaticcharge buildup on the nose cone of an artilleryprojectile or missile thereby preventing the arcing phenomena fromoccurring at the various gaps in the segmented antenna system due tocorona discharges at the front portion of the nose cone.

Another closely related but yet still significant object of thisinvention is the provision of a nose cone for proximity fuzes which iscapable of preventing premature functioning of fuzes due to coronadischarges.

A still further object of this invention is the provision of awindshield for proximity fuzes having a coating thereon and capable ofwithstanding high temperatures encountered during flight and havingsufficient erosion resistance to the air during flight.

An additional object of the invention is the provision of a coatedwindshield for proximity fuzes wherein the coating can be applied andcured at low temperatures thereby not causing any damage to electricalcomponents and/or the proximity fuze located within the nose cone.

The invention will be better understood and objects other than those setforth above will become apparent after reading the following detaileddescription of preferred, yet illustrative, embodiments hereof.

BRIEF SUMMARY OF THE INVENTION It has now been discovered that these andother objects may be accomplished by employing a windshield structurefor proximity fuzes capable of rendering harmless corona dischargestherefrom due to the buildup of static electrical charge on the surfacethereof resulting in the premature functioningof said fuzes whichcomprises, in combination, a conical nose portion and a cylindrical baseportion. The conical windshield comprises an electrically conductivesurface capable of withstanding and rapidly dispersing electricalcharges on said surface and having a surface resistivity of generallybetween 1 and 200 megohms per square and usually between about 1 and 40megohms per square.

The provisions of partially conducting surfaces for Windshieldscontaining proximity fuzes therein is particularly significant becausethe dissipation of static charges on the surface of the nose coneresults in the corona discharge becoming harmless thereby avoidingpremature firings of the fuze circuit due to arcing on the segmentedantenna located within the nose cone.

DETAILED DESCRIPTION OF THE INVENTION The conductive coating applied tothe nose cone is a resin-based material containing a conductivematerial, e.g., carbon. The resin selected according to this preferredembodiment of the invention should satisfy the following criteria:

1. Can be dispersed with the conductive material;

2. Can be rendered slightly electrically conductive;

3. Can be easily adhered to the surface of the windshield;

4. Does not degrade over long periods of time, etc.

launcher;

6. Not soften or vaporize during the first few seconds when thewindshield will see about 450 C. in flight from the gun barrel. (A heatdeflection temperature of about 150 C. helps withstand this initial hightemperature environment.)

Although resins having the above properties can be readily determined bythose skilled in the art, one resin which has been found to beparticularly useful in the practice of this embodiment of the inventionincludes epoxy based resins, e.g., Epon 828 or Epon 1001 (i.e.,condensation products of epichlorohydrin and bisphenol-A). Other resinswhich are believed to be useful in the practice of this inventioninclude (1) phenolic based resins, e.g., Electro-Science Labs phenolicresin in RS150 series (i.e., condensation reaction of a phenol and analdehyde plus an acid or base catalyst; (2) butyl based resins, e.g.,butyl rubber or buna-S rubber; (3) silicone based resins, e.g.,Dow-Comings 806A Resin (i.e., cohydrolyzing mixtures of RxSiCly where Ris usually methyl, phenyl or vinyl and x y 4); and (4) polyimide basedresins, e.g., DuPonts SP1 or PI- 2501 or Monsantos AF-R2009 or Skybond700 (i.e., reaction between an aromatic dianhydride and an aromaticdiamine).

In order to impart the desired properties to nose cones, a preferredembodiment of this invention relates to the coatings of the surface ofanose cone. According to this preferred embodiment of the invention,compositions useful for coating the nose cone comprise l) a base resinhaving the properties set forth above, (2) an inert volatile solvent,(3) a curing agent for said resin capable of imparting a heat deflectiontemperature for the cured coating of at least about 120 C. andpreferably between about 150 C. and 400 C., and (4) a powdered orfibrous conductive material.

The inert volative diluents or solvents are utilized to facilitate theapplication of smooth and even coatings on a substrate by means ofconventional coating techniques including painting, spraying, dipping,screening, etc. Suitable diluents or solvents include ketones (e.g.,methyl ethyl ketone and methyl isobutyl ketone), aromatics (e.g.,benzene, toluene, xylene), alcohols (e.g., butanol and isopropanol),esters (e.g., ethyl acetate and butyl acetate), saturated hydrocarbons,cyclic hydrocarbons and mixtures thereof. These may be used in amountsof up to about 33 to 67 percent of the weight of the composition,depending on how the coating is to be applied and the resin used. (About50 percent is preferred).

The curing agents useful in the preferred epoxy resin based compositionsof the present invention in order to form the desired coatings on nosecones include various types with the selection of the particular curingagent dependent upon the desired pot life of the resin and imparting asuitable heat deflection temperature to the cured temperature of atleast about 150 C. The curing agent selected should also enable cures atlow temperatures, e.g., cone-surface temperature of 130 C. for severalminutes produced by infrared lamps, where necessary, in order to protectany sensitive equipment located within the nose cone. Such lowtemperature cures' are particularly important when coatings are beingapplied to nose cones having proximity fuzes located therein andotherwise ready for use. When coatings are applied to the windshieldprior to fuze assemblage, longer curing times are permissible. Dependingon the resistance of the windshield material to continuous heat, highercuring temperatures may be permissible.

Examples of suitable curing agents for epoxy resins includediethylenetriamine, 2-ethyl-4-methylimidazole, diethylaminopropylamineand other conventionally used curing agents for epoxy resins.Cross-linking or final polymerization of phenolic resins are produced bycatalysts or may require heat. Cures of butyl based resins, siliconebased resins and polyimide based resins can be achieved in accordancewith conventional methods to produce a resin having the various desiredproperties discussed above.

When curing agents are employed in the practice of this invention, theyare essentially conventionally used curing agents for the particularresin employed in the practice of this invention. The curing agents areemployed in amounts effective for obtaining the desired cured resinhaving a heat deflection temperature of at least about C., butpreferably higher. The amount of curing agent employed is also dependentupon the amount of conductive material employed. For example, the amountof curing agent will be increased according to the amount of carbonemployed as the conductive material. Carbon has a high surface area andadsorbs the curing agent thereby necessitating the use of additionalamounts thereof.

The conductive material employed in the coating compositions of thisinvention for application to the surface 3 of the windshield orincorporated directly into the surface material of the nose cone withoutapplication of any coating thereon, includes a highly conductivematerial in a powdered or fibrous form, e.g., carbon black. Aparticularly useful form of carbon black is oil furnace carbon blackhaving a high surface area.

The amount of carbon employed is generally sufficient to impart aresistivity of from at least about 1.0 megohm to no more than 40 megohmson the surface of the windshield. Generally, from about 1 to about partsof carbon areused per 100 parts by weight of 5 tion shown and describedherein for obvious modificaresin and preferably between about 2 and 4parts of tions will occur to persons skilled in the art. carbon per 100parts by weight of resin when an epoxy Accordingly, what is claimed is:resin is used in the practice of this invention. 1. A windshield forproximity fuzes capable of with- When resin coatings are applied to thesurfaces of standing the buildup of static electrical charges on theWindshields, it is usually desired to first clean the windto surfacethereof resultingin the premature functioning shield. This can beaccomplished by first rubbing the of said fuzes, comprising incombination a conical windshield with acetone for degreasing the coneand windshield portion and a cylindrical base portion, said thereafterrubbing said windshield with a cheese cloth conical windshield portioncomprising an electrically soaked with a liquid coating composition inorder to inconductive surface capable of withstanding and rapidly sureeven wetting and coverage of the windshield surl5 dispersing electricalcharges on said surface and having face. a surface resistivity ofbetween about 1 and 200 megohms per square. EXAMPLES 2. A windshieldstructure of claim 1 wherein said The formulations set forth in thetable below are ilconical windshield portion has a surface resistivityof lustrative of several preferred epoxy based resin comabout 1.0 tomegohms per square and a heat deflecpositions that can be applied toWindshields in order to tlon temperature of atleast ab out llQf C.obtain the desired properties discussed hereinabove. Q Ihe windshieldstructure of claim l where in the TABLE Formulation 1A 1B 1c lD ll m w VVI Number of Components to gun l l l l l l l 1 First Component MixtureResin type Epon Epon 828 Epon 828 Epon 828 Epon I001 Epon l00l Epon i001Epon i001 Epon i001 828 Solvent mixture MIBK MIBK MIBK- MIBK- MlBK-MIBK- MIBK- MIBK- MIBK- lBA lBA lBA/X lBA/X IBA/X /BA/X lBA/X (/50)(50/50) (35/15/50 (35/15/50 (35/ 15/50 35/15/50) (35/ 15/50 Solvent/100100 50 pts l00 50 pts 200 pts 200 pts 120 pts 90 pts [l5 pts parts resinpts pts Carbon/lOO 4 pts 4 pts 4 pts 4 pts 4 pts 4 pts 3 pts 3 pts 3.3pts parts I'BSln Curing agent/100 EMl EMl EMl EMl DETA EMl EMl EM] partsresin (l0) (10 pts) (10 pts) (10 pts) (5 pts) (10 pts) (10 pts) (10 pts)pts Flow agent/I00 5 pts 5 pts 5 pts 5 pts 5 pts parts resinDefoamer/IOO 0.3 pts 0.3 pts 0.3 pts 0.3 pts 0.24 pts parts I'ESH'ISecond Component Mixture Solvent/100 75 pts parts resin Curing agcnt/lOOEMl parts resin (25 pts) MIBK methylisobutylketone BA hutylalcohol Xxylene EMl 2,4-ethylmethylimidazole DETA dicthylenetriaminc Carbonconductive (Vulcan XC-72R) Flow Agent Beetle 216-8 Defoamer PC4344 aflow agent to control the flow of coating over the surface of the nosecone and prevent cratering.

It should be understood that the invention is not limited to the exactdetails of construction and formulaelectrically conductive surface ofsaid conical windshield portion consists essentially of a conductivematerial dispersed throughout the surface of said windshield.

4. The windshield structure of claim 1 wherein said conical windshieldportion comprises a coating of a temperature resistant, electricalinsulating plastic material having a conductive material dispersedtherein, said coating covering at least a portion of the surface of saidwindshield.

5. The windshield structure of claim 4 wherein said plastic material isselected from the group consisting of epoxy, phenolic, butyl, silicone,and polyimide based resins.

6. A composition useful for forming a coating on Windshields forproximity fuzes comprising: (1) a base resin which can be easily adheredto the surface of the windwhield and does not degrade over long periodsof time; (2) an inert volatile solvent; and (3) a powdered or fibrousconductive material. I

7. A composition according to claim 6 wherein said base resin is anepoxy resin.

8. A composition according to claim 7 further comprising a curing agentfor said resin and capable of imparting a heat deflection temperaturefor the cured coating of at least about 120 C.

9. A composition according to claim 8 wherein said curing agent isselected from the group consisting of diethylenetriamine,2-ethyl-4-methylimidazole or diethylaminopropylamine.

10. A composition according to claim 6 wherein said inert volatilesolvent is selected from the group consist- 1. a solid epoxy resin;

2. 1 15 parts per parts resin of a solvent mixture consisting of about35 percent methylisobutylketone, 15 percent butyl alcohol and 50 percentxylene;

3. about 3.3 parts carbon black per 100 parts resin;

4. about 10 parts 2,4-ethylmethylimidazole per 100 parts resin;

5. about 5 parts of a flowing agent per 100 parts resin; and

6. about 0.24 parts defoaming agent per 100 parts resin.

1. A windshield for proximity fuzes capable of withstanding the buildupof static electrical charges on the surface thereof resulting in thepremature functioning of said fuzes, comprising in combination a conicalwindshield portion and a cylindrical base portion, said conicalwindshield portion comprising an electrically conductive surface capableof withstanding and rapidly dispersing electrical charges on saidsurface and having a surface resistivity of between about 1 and 200megohms per square.
 2. 115 parts per 100 parts resin of a solventmixture consisting of about 35 percent methylisobutylketone, 15 percentbutyl alcohol and 50 percent xylene;
 2. A windshield structure of claim1 wherein said conical windshield portion has a surface resistivity ofabout 1.0 to 40 megohms per square and a heat deflection temperature ofat least about 120* C.
 3. The windshield structure of claim 1 whereinthe electrically conductive surface of said conical windshield portionconsists essentially of a conductive material dispersed throughout thesurface of said windshield.
 3. about 3.3 parts carbon black per 100parts resin;
 4. about 10 parts 2,4-ethylmethylimidazole per 100 partsresin;
 4. The windshiEld structure of claim 1 wherein said conicalwindshield portion comprises a coating of a temperature resistant,electrical insulating plastic material having a conductive materialdispersed therein, said coating covering at least a portion of thesurface of said windshield.
 5. The windshield structure of claim 4wherein said plastic material is selected from the group consisting ofepoxy, phenolic, butyl, silicone, and polyimide based resins.
 5. about 5parts of a flowing agent per 100 parts resin; and
 6. about 0.24 partsdefoaming agent per 100 parts resin.
 6. A composition useful for forminga coating on windshields for proximity fuzes comprising: (1) a baseresin which can be easily adhered to the surface of the windwhield anddoes not degrade over long periods of time; (2) an inert volatilesolvent; and (3) a powdered or fibrous conductive material.
 7. Acomposition according to claim 6 wherein said base resin is an epoxyresin.
 8. A composition according to claim 7 further comprising a curingagent for said resin and capable of imparting a heat deflectiontemperature for the cured coating of at least about 120* C.
 9. Acomposition according to claim 8 wherein said curing agent is selectedfrom the group consisting of diethylenetriamine,2-ethyl-4-methylimidazole or diethylaminopropylamine.
 10. A compositionaccording to claim 6 wherein said inert volatile solvent is selectedfrom the group consisting of ketones, aromatics, esters, saturatedhydrocarbons, cyclic hydrocarbons, alcohols and mixtures thereof.
 11. Acomposition according to claim 6 wherein said conductive material iscarbon black.
 12. A composition according to claim 6 comprising: